1. Field of the Invention
The present invention relates to a frame with a new structure where a screen to be used in screen printing is stretched.
The invention also relates to an extension tool for the purpose of stretching a sheet-like material, e.g., a sheet-shaped or mesh material made of metal, resin, etc. to be used in screen printing, a sheet-shaped material such as a canvas to be used for a texture in oil painting, or a sheet-shaped material such as leather to be stretched on a percussion instrument body such as a drum.
2. Description of the Related Art
A screen printing screen sheet with a relatively simple structure has been conventionally used, in which a metal mesh with lower elasticity for a portion where an image is to be formed is arranged at the central portion of the screen and a mesh with a relatively higher elasticity is disposed on the periphery of the portion where the image is to be formed as a support member.
For a screen, elasticity and expandability are entirely different, depending on the size of the portion where the image is to be formed or depending on the material used for the screen. In this respect, it is extremely necessary to adjust the screen for preparing the screen to suit the purpose required on the object to be printed, and this adjustment is difficult to carry out.
The screen for screen printing is stretched by applying tension to the screen. For this reason, a screen frame must have sufficient strength to endure the tension, and wooden or metal material having high strength is used. Accordingly, the screen frame is weighty and bulky.
A screen frame needs a large-scale pulling means when adjusting the length of the screen frame sides, and because a large-scale pulling means must be used, the structure is not very convenient to handle.
Also, it is not always easy to stretch the screen or to adjust the tension on the spread screen by combining the screen frame for freely adjusting the length of each side of the screen frame with a tool used to fix the screen. Also, it is difficult to freely attach or remove the means to which the screen is fixed.
Further, in a case where the object to be printed is distorted or has unevenness in the extension of the screen, or in a case where distortion or deviation occurs in an embossed printing, it is difficult to attain a high degree of accuracy in printing by compensating or adjusting based on these problems.
Once the screen has been fixed on the screen frame, it is further difficult to adjust the distortion or deviation of images.
The conventional tool for stretching a sheet-shaped material comprising an expandable frame body has been practiced as adjusting the positions of four sides of the frame respectively to change the distance between the frame sides so as to adjust the tension of the sheet-shaped material stretched on the extension tool.
A frame with a plurality of mechanisms for finely adjusting the tension on the stretched screen is disclosed in Japanese Laid-Open Utility Model Application No. 1-141027, Japanese Laid-Open Utility Model Application No. 55-136533 and International Patent Publication WO 92/03231.
A frame in which a screen is fixed on a support frame by an anchor pin to add tension in advance to the screen, the support frame is attached to an extension frame and the tension is adjusted by a screw, is disclosed in U.S. Pat. No. 3,482,343, U.S. Pat. No. 3,485,165 and U.S. Pat. No. 6,427,588.
A frame for stretching a screen, in which the screen is fixed on a support frame by using grooves and fixing members, the support frame is mounted on the frame for stretching the screen and the length of frame sides is changed by using a screw mechanism or a fluid cylinder on the frame, is disclosed in U.S. Pat. No. 5,113,611.
A frame, in which the tension is finely adjusted by rotating the frame where the screen is stretched, is disclosed in U.S. Pat. No. 5,076,162, U.S. Pat. No. 5,271,171 and U.S. Pat. No. 5,265,534.
A frame, in which tension is added in advance by fixing the screen on a support frame by using an adhesive agent and the support frame is attached to the frame by means of an anchor and the frame is finely adjusted by rotating a screw or a frame member, is disclosed in U.S. Pat. No. 5,802,971.
In these types of screen extension frames, there are many points to be adjusted. Also, when adjustment is made at a point, the tension on other points is also changed, and thus it is difficult to stretch the sheet-shaped material over its entirety under the tension as desired. This means that a long period of time is required for adjusting the tension. Further, when the screen is mounted on the frame, a lot of time and labor are required for the operations of mounting and removing.
Under such circumstances, the present inventor has developed, as shown in International Patent Publication WO 02/55304, an extension tool with a new structure, in which it is possible to easily adjust the tension by using four mechanisms.